1. Field of the Invention
The invention relates to an apparatus and method for verifying optical fiber connectivity using an OTDR Test Receiver including receive fibers having different lengths.
2. Description of Related Art
Testing regimens for fiber optic cables normally include a determination of two key measurables. The first measurable is a transmission loss, or other similar parameters, of each fiber optic cable. The second measurable is a verification of the connectivity of each fiber, i.e., verifying that each fiber terminates at an expected port at each end of the cable.
Various testing devices for determining these measurables are known in the related art, including an Optical Time Domain Reflectometer (OTDR) and Optical Loss Test Sets (OLTS).
An OTDR generally is connected to a first end of a fiber to be tested, and transmits pulsed light signals along the fiber. Reflections and/or backscattering occur within the fiber due to discontinuities such as connectors, splices, bends and faults. The OTDR detects and analyzes these reflections and/or backscattering, and provides a OTDR trace that shows positions of discontinuities and an end-to-end loss in the fiber.
However, OTDRs require launch and receive test cables to effectively measure a full, end-to-end, transmission loss of the fiber optic line, since “deadzones” (caused by interference by closely spaced discontinuities) may obscure such a measurement. The launch test cable connects the OTDR to the first end of the fiber to be tested, and reveals the insertion loss and reflectance at the first end. Similarly, the receive test cable is connected to second end of the fiber to be tested, and reveals the insertion loss and reflectance at the second end, along with verifying the connectivity of the fiber optic line.
On the other hand, an OLTS provides a light source connected to one end of the fiber to be tested, which emits a signal that consists of a continuous wave at a specific wavelength. At the other end of the fiber to be tested is an optical power meter, which detects and measures the power level of the signal emitted from the light source. Such an OLTS can measure loss in the fiber to be tested by determining a difference in power level of the signal measured at the transmitting and receiving ends. Further, when utilizing an OLTS, a test result in which the light source and optical power meter communicate with each other also verifies the connectivity of the fiber to be tested.
Unfortunately, there are problems with both OTDR and OLTS. For example, both require either: (1) two technicians (i.e., one at each end of the fiber to be tested); or (2) one technician that travels back and forth between the two ends of the fiber to be tested, to test each fiber. The use of two technicians is costly and personnel-restricted, while the use of one technician traveling back and forth between the two ends of the fiber to be tested is so time consuming as to be impractical.
Further, with specific regard to OTDR, there is no particular way for the OTDR to identify which fiber is being tested. Thus, the technician must be very attentive to ensure that the proper fibers are tested, and the proper results are recorded.